Debunking the ‘five-second rule’

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The educational YouTube channel Vsauce took its turn recently at debunking the stubbornly persistent myth of the “five-second rule.”

Cooks, please take note.

The five-second rule is the belief that if you pick up food within five seconds of unintentionally dropping it on the floor, the food remains relatively uncontaminated with bacteria and other nasty microbes, and is thus safe to eat.

In 2003, an enterprising student researcher conducted a survey and found that 56 percent of men and 70 percent of women believed in this rule. (She also found that cookies and candy were more likely to be retrieved from the floor than cauliflower and broccoli.)

It should really be the “don’t-touch-food-that’s-fallen-on-the-floor rule,” he says.

It’s true that, for reasons that have to do with intermolecular forces (which Stevens does a remarkably clear job of explaining), the longer a food — say, a banana — is on the floor, the more germs it will pick up.

But that banana can absorb a lot of unpleasant pathogens within five seconds.

In a 2006 study, researchers dropped bread and bologna onto surfaces that had been contaminated with salmonella bacteria eight hours earlier. The food picked up 150 to 8,000 bacteria within five seconds. When the food was allowed to remain on the surface for a full minute, the number of bacteria increased tenfold.

Another finding from that study: Salmonella bacteria remained on wood, tile and nylon-carpet surfaces for at least four weeks after it had been placed there.

Keeping your home’s floors (and other surfaces) clean will help, of course. But you’ll have to be scrubbing those floors quite frequently. For, as Stevens also points out, University of Arizona researchers have found that 93 percent of shoes are contaminated with fecal matter.

Yuck.

OK. Yes, it’s true that bacteria and other microbes are everywhere and that our immune systems usually do an amazing job at keeping those germs from harming us. And, yes, some scientists believe that our anxiety about avoiding all germs is overblown and may itself be making us sick. Exposure to certain pathogens is actually good for us, they argue.